The present invention relates to a transmission control device for controlling the operation of a transmission system which includes a main transmission portion and a sub transmission portion.
Conventionally, a transmission may be composed of a combination of a main transmission portion and a sub transmission which is capable of selective manual change-over of transmission gears. For example, a transmission may be composed of: a controller which controls in accordance with various factors representing the state of running, e.g., vehicle running speed or throttle opening of the engine; a hydraulic controller which is controlled on the basis of the output of the controller; a main transmission which serves as a main transmission portion, and which has a plurality of transmission gears controlled by the hydraulic controller; and a sub transmission which serves as a sub transmission portion, which has an input shaft constituted by the output shaft of the main transmission and which is capable of manually shifting operation. Such a transmission is so designed that, even while the transmission gear of the sub transmission is being changed, the transmission gear of the main transmission is still changed in accordance with various factors representing the state of running, e.g., vehicle running speed or throttle opening of the engine, and that, even while the transmission gear of the main transmission is being changed, the transmission gear of the sub transmission may be manually changed.
As described above, in a conventional transmission, while one transmission is in operation, the other transmission may sometimes be operated independently. Since fluctuation of the output torque due to the shifting operation of the sub transmission is caused at this time together with fluctuation of the input torque caused by the shifting operation of the main transmission, transmission shock is disadvantageously amplified. Furthermore, in a four-wheel drive automatic transmission in which the transmission gears of the main and sub transmissions are controlled by a hydraulic controller, if the shifts of the main transmission and the sub transmission are synchronized, the supply of the working oil to the hydraulic servomotors for the purpose of shift by means of the main transmission and the supply of the working oil to the hydraulic servomotors for the purpose of shift by means of the sub transmission are carried out simultaneously. As a result the oil pressure supplied to each hydraulic servomotor is lowered, and optimum shifting characteristics are not obtained.